The invention concerns a method for reducing pollution emissions, especially emissions of pyrolysis products, from the metal casting cases used in foundry practice. The invention also concerns metal casting cases for carrying out the method of the invention.
In metal foundries, emissions from metal casting molds are a significant source of odors as well as pollutants that may have important consequences to human health and the environment. The high temperatures required in metal casting cause large numbers of mainly organic substances in the form of pyrolysis products to be released from the metal casting molds or flasks. These products arise chiefly by thermal decomposition of the core mold material and of the additives used in the molding sand in metal casting The decomposed and volatilized compounds escape as noncombusted hydrocarbons, gases, aerosols, smoke, or dust.
The pollutant emissions arising during metal casting are released mainly in the casting line itself as well as in the cooling line and at the shakeout station, in other words, starting directly with the operation of pouring the molten metal. When metal casting cases are used, the pollutants escape, for example, through the fitting edge of the two halves of the casting mold. Additional release of a relatively large amount of emissions occurs during removal of the hot casting from the metal casting mold (shakeout station).
Occasionally, accidental combustion of the escaping emissions occurs or combustion is initiated by a pilot flame. However, this combustion occurs only if the local concentration, temperature, and calorific value of the emissions will allow this to occur.
Improved mold materials were developed to reduce the existing emissions load. Furthermore, legal emissions requirements were complied with by exhaust gas purification, for example, by expensive filtration systems, scrubbers, and biofilters. These systems have the disadvantage of high material and maintenance expenses. Moreover, the efficiency of these kinds of systems often fails to meet statutory requirements.
For example, DE 43 27 396 A1 describes direct exhausting of the pyrolysis products that are released in a casting operation and that form the pollutant emissions, collecting them in a collecting tank maintained at a negative pressure, and mixing them with secondary air, and then passing the exhaust air that has been diluted in this way through a separation stage before releasing it into the open atmosphere. A system of this type for catching, exhausting, and separating pyrolysis products is complicated and thus expensive.
Pyrolysis products that are a source of odors and of pollutants that are harmful to human health and the environment are also produced with the use of investment patterns made of vaporizable foam (CH 442 628 and DE 37 07 581 C2), since this mold material can be vaporized only “practically” residue-free, and, in addition, the gases formed during the pouring of the molten charge are drawn off through degassing channels and released into the atmosphere Environmental protection and humanization of the workplace are also becoming increasingly important in the foundry sector (DE 42 26 327 A1, DE 32 46 324 C2, and DE 43 27 292 C2). Further prior art methods are specified in U.S. Pat. No. 4,266,595.